/**
 * Copyright 2010-2018 the original author or authors.
 * <p>
 * Licensed under the Apache License, Version 2.0 (the "License");
 * you may not use this file except in compliance with the License.
 * You may obtain a copy of the License at
 * <p>
 * http://www.apache.org/licenses/LICENSE-2.0
 * <p>
 * Unless required by applicable law or agreed to in writing, software
 * distributed under the License is distributed on an "AS IS" BASIS,
 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 * See the License for the specific language governing permissions and
 * limitations under the License.
 */
package org.mybatis.spring.batch;

import org.apache.ibatis.executor.BatchResult;
import org.apache.ibatis.session.ExecutorType;
import org.apache.ibatis.session.SqlSession;
import org.apache.ibatis.session.SqlSessionFactory;
import org.mybatis.logging.Logger;
import org.mybatis.logging.LoggerFactory;
import org.mybatis.spring.SqlSessionTemplate;
import org.springframework.batch.item.ItemWriter;
import org.springframework.beans.factory.InitializingBean;
import org.springframework.core.convert.converter.Converter;
import org.springframework.dao.EmptyResultDataAccessException;
import org.springframework.dao.InvalidDataAccessResourceUsageException;

import java.util.List;

import static org.springframework.util.Assert.isTrue;
import static org.springframework.util.Assert.notNull;

/**
 * {@code ItemWriter} that uses the batching features from
 * {@code SqlSessionTemplate} to execute a batch of statements for all items
 * provided.
 * <p>
 * Provided to facilitate the migration from Spring-Batch iBATIS 2 writers to MyBatis 3.
 * <p>
 * The user must provide a MyBatis statement id that points to the SQL statement defined
 * in the MyBatis.
 * <p>
 * It is expected that {@link #write(List)} is called inside a transaction. If it is not
 * each statement call will be autocommitted and flushStatements will return no results.
 * <p>
 * The writer is thread safe after its properties are set (normal singleton
 * behavior), so it can be used to write in multiple concurrent transactions.
 *
 * MyBatis 批量写入器
 *
 * @author Eduardo Macarron
 *
 * @since 1.1.0
 */
public class MyBatisBatchItemWriter<T> implements ItemWriter<T>, InitializingBean {

    private static final Logger LOGGER = LoggerFactory.getLogger(MyBatisBatchItemWriter.class);

    /**
     * SqlSessionTemplate 对象
     */
    private SqlSessionTemplate sqlSessionTemplate;

    /**
     * 语句编号
     */
    private String statementId;

    /**
     * 是否校验
     */
    private boolean assertUpdates = true;

    /**
     * 参数转换器
     */
    private Converter<T, ?> itemToParameterConverter = new PassThroughConverter<>();

    /**
     * Public setter for the flag that determines whether an assertion is made
     * that all items cause at least one row to be updated.
     *
     * @param assertUpdates the flag to set. Defaults to true;
     */
    public void setAssertUpdates(boolean assertUpdates) {
        this.assertUpdates = assertUpdates;
    }

    /**
     * Public setter for {@link SqlSessionFactory} for injection purposes.
     *
     * @param sqlSessionFactory a factory object for the {@link SqlSession}.
     */
    public void setSqlSessionFactory(SqlSessionFactory sqlSessionFactory) {
        if (sqlSessionTemplate == null) {
            this.sqlSessionTemplate = new SqlSessionTemplate(sqlSessionFactory, ExecutorType.BATCH);
        }
    }

    /**
     * Public setter for the {@link SqlSessionTemplate}.
     *
     * @param sqlSessionTemplate a template object for use the {@link SqlSession} on the Spring managed transaction
     */
    public void setSqlSessionTemplate(SqlSessionTemplate sqlSessionTemplate) {
        this.sqlSessionTemplate = sqlSessionTemplate;
    }

    /**
     * Public setter for the statement id identifying the statement in the SqlMap
     * configuration file.
     *
     * @param statementId the id for the statement
     */
    public void setStatementId(String statementId) {
        this.statementId = statementId;
    }

    /**
     * Public setter for a converter that converting item to parameter object.
     * <p>
     * By default implementation, an item does not convert.
     *
     * @param itemToParameterConverter a converter that converting item to parameter object
     * @since 2.0.0
     */
    public void setItemToParameterConverter(Converter<T, ?> itemToParameterConverter) {
        this.itemToParameterConverter = itemToParameterConverter;
    }

    /**
     * Check mandatory properties - there must be an SqlSession and a statementId.
     */
    @Override
    public void afterPropertiesSet() {
        notNull(sqlSessionTemplate, "A SqlSessionFactory or a SqlSessionTemplate is required.");
        isTrue(ExecutorType.BATCH == sqlSessionTemplate.getExecutorType(), "SqlSessionTemplate's executor type must be BATCH");
        notNull(statementId, "A statementId is required.");
        notNull(itemToParameterConverter, "A itemToParameterConverter is required.");
    }

    /**
     * {@inheritDoc}
     */
    @Override
    public void write(final List<? extends T> items) {
        if (!items.isEmpty()) {
            LOGGER.debug(() -> "Executing batch with " + items.size() + " items.");

            // 遍历 items 数组，提交到 sqlSessionTemplate 中
            for (T item : items) {
                sqlSessionTemplate.update(statementId, itemToParameterConverter.convert(item));
            }
            // 执行一次批量操作
            List<BatchResult> results = sqlSessionTemplate.flushStatements();

            if (assertUpdates) {
                // 如果有多个返回结果，抛出 InvalidDataAccessResourceUsageException 异常
                if (results.size() != 1) {
                    throw new InvalidDataAccessResourceUsageException("Batch execution returned invalid results. " +
                            "Expected 1 but number of BatchResult objects returned was " + results.size());
                }

                // 遍历执行结果，若存在未更新的情况，则抛出 EmptyResultDataAccessException 异常
                int[] updateCounts = results.get(0).getUpdateCounts();
                for (int i = 0; i < updateCounts.length; i++) {
                    int value = updateCounts[i];
                    if (value == 0) {
                        throw new EmptyResultDataAccessException("Item " + i + " of " + updateCounts.length
                                + " did not update any rows: [" + items.get(i) + "]", 1);
                    }
                }
            }
        }
    }

    private static class PassThroughConverter<T> implements Converter<T, T> {

        @Override
        public T convert(T source) {
            return source;
        }

    }

}
